1. Technical Field
The present invention pertains to temperature control systems for infused liquids, such as the types disclosed in U.S. patent application Ser. Nos. 09/380,507, entitled “Method and Apparatus for Pressure Infusion and Temperature Control of Infused Liquids” and filed Apr. 24, 2000, and Ser. No. 10/095,100, entitled “Method and Apparatus for Controlling Pressurized Infusion and Temperature of Infused Liquids” and filed Mar. 12, 2002, the disclosures of which are incorporated herein by reference in their entireties. In particular, the present invention is directed toward a portable system that controls the temperature of a fluid within a flexible bag or container during infusion of the fluid from the container to a patient.
2. Discussion of Related Art
Generally, various items are required to be heated prior to use in a medical procedure, or in support of related medical care, to prevent injury to a patient. These items typically include intravenous solutions, irrigation fluids, surgical instruments, bottles, and blankets. Intravenous (IV) fluids, for example, are typically stored in a cool environment and, consequently, require heating to precise temperatures to prevent thermal shock and injury from occurring during infusion of the fluid into a patient. Similarly, irrigation fluids can be warmed or cooled to various temperatures depending upon their intended use. These types of fluids are typically provided to a patient utilizing a flexible bag or container filled with the fluid and delivered via a fluid line that conveys the fluid from the bag to the patient.
Some medical items can only be heated for a limited period of time, or in accordance with controlled warming cycles, in order to avoid adversely affecting their effectiveness. For example, some fluids, such as whole blood or fluids containing medication, should be warmed evenly to a specific temperature and can be rendered unusable or unsafe if all or a portion of the fluid is overheated.
In order to provide the necessary heated items for use in medical procedures, the related art provides several devices for regulating temperature of a fluid in an IV fluid bag. For example, U.S. Pat. No. 4,430,078 (Sprague) discloses a portable blood infusion pump designed to be employed in combination with a blood bag. The blood bag is located within a storage chamber that includes an inflatable bladder. Pressurized fluid is conducted within the inflatable bladder to press against the blood bag to enable discharge of the blood from the blood bag through a discharge conduit assembly. A container containing a supply of the pressurized fluid is mounted within the pump housing and is connected to the inflatable bladder. A pressure regulator is disposed in the housing to permit variance of pressure applied by the bladder against the blood bag in response to user manipulation of a knob. The pressure level applied by the bladder to the blood bag may be preset by a user via the knob while the regulator maintains the pressure level and automatically provides additional gas to the bladder in response to decreasing quantities of blood within the blood bag. An electrical heater apparatus may be included within the device to provide heat energy to the blood bag so as to warm the blood prior to being infused into a patient.
U.S. Pat. No. 5,125,900 (Teves) discloses a device for heating and pressurizing fluid filled containers. The device wraps around a flexible bag containing fluid to warm the fluid and to pressurize the bag so that warm fluid flows from the bag at a rate dependent upon the amount of pressure applied to the bag. The device includes a heating element that may be set at a preselected temperature and an inflatable bladder that may be inflated to a preselected pressure.
U.S. Pat. No. 5,420,962 (Bakke) discloses a system for warming blood or other liquids to body temperature for infusion into a patient. The system includes a blood warmer apparatus having a pair of closely spaced apart heat transfer plates, each of which forms one face of a housing containing flat vapor condensation heating units. A flat disposable heat exchanging blood warming envelope is held clamped between the heat transfer plates. An air heating unit in one of the apparatus housings includes a cool air inlet, heat transfer fins on the walls of the vapor condensation heater unit, a fan and guides for conducting air past those fins and a warmed air outlet. An external elongated insulated air hose is connected at one end to the warmed air outlet and extends to the patient. The blood flow line from the outlet of the heat exchanging envelope is positioned within the warmed air hose to maintain the physiologic temperature of the blood.
U.S. Pat. No. 5,733,263 (Wheatman) discloses an apparatus for heating fluid contained in one or more bags and delivering the fluid from at least one bag to a surgical patient. The apparatus includes a housing to enclose at least one bag containing fluid and having a door positioned to provide access to the housing interior. The apparatus further includes an inflatable bladder mounted in the housing interior and connected to a source of pressurized fluid for inflation. The inflatable bladder exerts force against at least one bag mounted within the housing. A regulator permits regulation of gas pressure to the bladder in response to user manipulation of a housing regulator knob. In addition, the apparatus includes a heater mounted adjacent the housing door in heat transfer relationship with the fluid and at least one bag.
U.S. Pat. Nos. 5,879,329 and 5,989,238 (Ginsburg) disclose a system for infusing a fluid into a patient. The system includes a fluid reservoir and a temperature-altering device in close proximity thereto. The temperature-altering device is employed to heat or cool the fluid to a desired temperature. A positive pressure device in the form of a bladder and pressure source may be provided to place the reservoir under positive pressure while at the desired temperature. The pressure source may be connected to a processor to control the total rate and volume of fluid introduced into the bladder, thereby controlling the rate and volume of fluid leaving the reservoir. A transfer member is further provided to transfer at least some of the fluid into the patient while at the desired temperature. In addition, the system may be portable for utilization in field applications.
U.S. Pat. No. 6,035,103 (Bakke) discloses a system for warming blood or other liquids to body temperature and maintaining the liquid at that temperature for infusion into a patient. The system includes a cylindrical condensation liquid heating chamber having an inner tubular air heater. A cylindrical heat retaining shell surrounds and is spaced from the outer wall of the heating chamber. A flat flexible heat exchanging liquid warming envelope is held clamped between the outer wall of the heating chamber and the surrounding shell. An external outer elongated air hose is connected at one end to a warmed air outlet from the air heater and extends to the patient and surrounds an inner elongated warm liquid flow line to maintain the temperature of the liquid.
U.S. Pat. No. 6,096,007 (Haan et al.) discloses a pressure container for applying pressure to a flexible bag received therein and filled with a medical fluid in order to deliver the fluid from the flexible bag. The pressure container includes a housing that has an opening for introduction of the bag, a cover for covering the opening, an aperture for leading a fluid discharge line of the bag out of the pressure container and a closure for sealed joining of the cover and housing. The housing may be configured as an upright hollow-cylindrical body closed at the bottom and open at the top, the cross-section of which has a flattened, oval shape and corresponds roughly to the cross-sectional contour of a bag. The two opposing large-area upright housing sidewalls each have, in mirror-image fashion, the shape of a segment of a cylindrical shell with lateral ends joined by joining segments. A heater may be provided on the housing.
The related art devices described above suffer from several disadvantages. In particular, the Teves and Haan et al. devices heat a particular bag surface or do not completely enclose a fluid bag within the device, thereby enabling skewed or non-uniform heating of IV fluid within the bag. Similarly, the Wheatman apparatus employs a heating element assembly located on the housing door that provides heat to one surface of the IV bag. These types of heating typically produce “hot” and/or “cold” spots within the IV fluid that may cause patients to receive the fluid at inappropriate temperatures, thereby risking injury to those patients.
In addition, the Bakke (U.S. Pat. Nos. 5,420,962 and 6,035,103), Sprague, Wheatman and Ginsburg devices typically house an IV fluid bag within a housing. Thus, these devices do not permit easy access and/or viewing of the bag during infusion. This typically requires medical personnel to repeatedly access the housing interior to monitor the bag (e.g., to determine the amount of fluid remaining within the bag and whether or not the bag needs to be replaced with a new bag) and/or increases the amount of time needed to replace an existing depleted or problematic bag with a new bag. The increased time needed to replace a bag may cause serious adverse conditions for a patient, especially during critical medical situations. In addition, the above devices do not provide a medical item temperature history. This enables use of medical items that may have been rendered unsafe or less effective during heating due to attainment of undesirable temperatures, thereby increasing risk of injury to a patient.